This is absolutely not related to the subject at hand though. If you're talking in a general case, it's because it is actually hard. Send the buffer to your gp

This is absolutely not related to the subject at hand though. If you're talking in a general case, it's because it is actually hard. Send the buffer to your gpu, have it execute the command, send it to your screen which probably has a CPU of its own. Pushing a pixel is hard, and you have to do it 60 times a second. That's also why you don't just push a pixel but the entire screen at once. How hard it is for you depends entirely on the API. While Direct3D/OpenGL expose all the details, others like XNA or even Javascript's canvas do it rather painlessly. What's really hard isn't pushing a pixel to the screen: it's doing it fast enough (i.e. same as your screen's refresh rate ideally) so that the user doesn't notice a visible delay. When 75% of the API is blocking AND you do work on the UI thread (Which is absolutely insane that browser developers haven't picked up this practice considering it's been advocated for more than 15 years on the native side of things), it's usually going to be visible.